Retinal nerve fibre layer imaging: Comparison of Cirrus optical coherence tomography and Heidelberg retinal tomograph 3

Background: The purpose of this study was to analyze the relationship between retinal nerve fibre layer thickness measured by spectral domain optical coherence tomography and confocal scanning laser ophthalmoscope. Design: Prospective, cross-sectional study. Hospital setting. Participants: One hundred seventy-three subjects (85 glaucoma and 88 normal subjects). Methods: One eye from each individual was selected randomly for imaging by the spectral domain Cirrus optical coherence tomography and Heidelberg retinal tomograph 3. Main Outcome Measures: Global thickness and measurements at the four quadrants around the optic disc. Results: Measurements as determined by Heidelberg retinal tomograph 3 were significantly larger than measurements done by Cirrus optical coherence tomography (respectively in mm, for global thickness: 200.0±87.2 and 80.7±14.7; for temporal quadrant: 75.3±31.9 and 59.1±13.8; for superior quadrant: 223.2±128.4 and 97.7±20.9; for nasal quadrant: 208.0±102.9 and 66.8±11.8; and for inferior quadrant: 224.4±116.9 and 99.1±26.6, for all P<0.01). Significant correlation was found for all measurements (P≤0.009), but a pattern of proportional bias was demonstrated. The agreement of categorical classification (within normal limits, borderline or outside normal limits) ranged between poor and fair. Conclusions: The thickness easurements by the two technologies are strongly correlated but significantly different. The differences are substantial and proportional to the retinal nerve fibre layer thickness. The normative diagnostic classification of the two technologies may not agree. The results preclude interchangeable use of these measurements in clinical practice.